#!/usr/bin/python2.7
"""Dynamic DNS script. Expects URLs from routers in the form
https://info.colgarra.priv.at/dyndns/dyndns.py?username=<username>&password=<pass>&hostname=<domain>&myip=<ipaddr>
"""

import re
import cgi
import pwd
from subprocess import call
import ipaddr


# Configuration
PASSWORD = 'hygCithOrs5'
ZONE = '.dyn.colgarra.priv.at'
DEBUG = False


# Just for debugging:
if DEBUG:
	import cgitb
	cgitb.enable()


fields = cgi.FieldStorage()

# the following fields are supported by most dyndns providers
# if a parameter is not provided, the .getvalue method returns None
username = fields.getvalue('username')
password = fields.getvalue('password')
hostname = fields.getvalue('hostname')
myip     = fields.getvalue('myip')
wildcard = fields.getvalue('wildcard')
mx       = fields.getvalue('mx')
backmx   = fields.getvalue('backmx')
offline  = fields.getvalue('offline')


try:
	# check username
	user_info = pwd.getpwnam(username) # returns a key error if the user does not exist
	if user_info.pw_uid < 1000:
		raise RuntimeError('Invalid user name')

	# check password
	if password != PASSWORD:
		raise RuntimeError('Invalid password')

	# check hostname
	if re.match(r'[-0-9a-z]+(\.[-0-9a-z]+)*$', hostname) is None:
		raise RuntimeError('Invalid host name')

	# strip zone
	hostname = hostname.strip()
	if hostname.endswith(ZONE):
		hostname = hostname[:-len(ZONE)]

	# check IP address
	ip = ipaddr.IPAddress(myip) # throws axception if the IP address is not valid
	if isinstance(ip, ipaddr.IPv4Address):
		type = 'A'
	elif isinstance(ip, ipaddr.IPv6Address):
		type = 'AAAA'
	else:
		raise RuntimeError('Unknown IP address type')

	# access granted
	print "Content-Type: text/html"
	print
	call(['sudo', '/usr/local/bin/nsupdate_dyndns', hostname, myip, type])
	print "OK"


except:
	# access denied
	print "Content-Type: text/html"
	print "Status: 403 Forbidden"
	print
	print "Denied"